Starting a turbine engine from a very low engine speed with limited rotational assistance can be very difficult. Turbine engine starts initiated at very low engine speeds typically result in a rapid increase in engine turbine temperature. When fuel is introduced into and burned within the engine combustor at a normal, continuous rate which is required to achieve proper fuel atomization, the reduced air flow that results from the low rotational speed of the fan and compressors, causes most of the energy produced during combustion to increase temperatures within the engine's turbine section rather than converting the energy to rotational acceleration of the turbine rotor. Often this results in the need to abort the start in order to avoid the risk of over-temperature damage to the engine components. Conventional engine starting operations require that turbine engine starts be initiated at a predetermined engine speed value which is designed for a standard engine starting operation without the risk of over-temperature damage caused by the reduced air flow. However, under certain conditions such as low batteries or poor “windmill” conditions, it is desirable to start an aircraft turbine engine from an engine speed which is initially below the normal engine start speed.
Accordingly, there is a need to provide an improved method of starting a turbine engine from a low engine speed.